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HomeMy WebLinkAboutLDS TEMPLE - PDP - PDP120029 - SUBMITTAL DOCUMENTS - ROUND 2 - REVISIONS (3)Terracon Consultants, Inc. 1901 Sharp Point Drive, Suite C Fort Collins, Colorado 80525 P [970] 484-0359 F [970] 484-0454 www.terracon.com January 8, 2013 The Church of Jesus Christ of Latter-day Saints 50 East North Temple, 10th Floor Salt Lake City, Utah 84150 Attn: Mr. John Stoddard P: (801) 249-7132 E: stoddardJB@ldschurch.org Re: Supplemental Geotechnical Engineering Recommendations Fort Collins Temple Southeast of South Timberline Road and East Trilby Road Fort Collins, Colorado Terracon Project No. 20115025 In this letter, Terracon Consultants, Inc. (Terracon) presents Supplemental Geotechnical Engineering Recommendations for the Fort Collins Temple. These recommendations supplement our Geotechnical Engineering Report; dated August 19, 2011(Project No. 20115025). Background Information In contacts with members of the project team, we were informed that the widening of South Timberline Road planned as part of the project will require reconfiguration of the existing drainage swale along the eastern side of the roadway south of Majestic Drive as well as construction of curb, gutter and new pavements. We were informed that the City of Fort Collins has expressed concerns about slope erosion and other issues at this location. Terracon was requested to provide geotechnical engineering recommendations to address the City of Fort Collins concerns and recommendations to be considered by other members of the design team for this section of site development. To assist with our analysis, we were provided with conceptual civil drawings related to the roadway widening showing the existing site grades as well as proposed site grades and planned construction. The conceptual drawings indicate the existing slope on the eastern side of the drainage swale south of Majestic Drive and the Temple property and north of Rock Castle Lane is as steep as about 2:1 (h:v). New construction will require placing fill into the existing drainage swale and construction of curb and gutter at the toe of the slope. Following construction of the new curb, gutter and roadway, the backfill placed behind the new curb and gutter will be blended into the existing slope. The roadway and curb and gutter construction may require minor temporary excavation into the existing slope. Supplemental Geotechnical Engineering Report Fort Collins Temple ■ Fort Collins, Colorado January 8, 2013 ■ Terracon Project No. 20115025 Responsive ■ Resourceful ■ Reliable 2 Geotechnical Recommendations We did not complete exploratory borings within the existing drainage swale along the proposed widening alignment. However, our experience indicates the subgrade soils that will provide support of the proposed curb, gutter and pavements along the drainage swale are likely clayey soils similar to the surficial soils within the Temple site. These soils may be moist and may require stabilization prior to placement of new fill and construction of the proposed improvements. Prior to fill placement and roadway construction, we recommend stripping and removing existing vegetation and other deleterious materials from below the proposed pavements and areas planned to receive fill. If unstable conditions are encountered or develop during construction, workability may be improved by scarifying and drying; however, allowing the clays to dry out below the optimum moisture content is not recommended. As an alternative, affected areas could be over-excavated and replaced with granular materials and/or non- to low expansive imported materials. If necessary, crushed concrete and/or rock could be tracked or “crowded” into the unstable subgrade until a stable working surface is attained. In order to reduce the risk for erosion of the compacted fill placed behind the proposed curb and gutter, we recommend placing fill and/or backfill in 6-inch maximum lifts, moisture conditioning and compacting as described below. Engineered fill should be placed and compacted in horizontal lifts, using equipment and procedures that will produce recommended moisture contents and densities throughout the lift. Item Description Fill lift thickness 6 -inches or less in loose thickness Compaction requirements (clay) 95 percent of the maximum dry unit weight as determined by ASTM D 698 Moisture content cohesive soil (clay) -1 to +2% of the optimum moisture content in pavement areas Moisture content cohesionless soil (sand) -3 to +3 % of the optimum moisture content 1. We recommend engineered fill be tested for moisture content and compaction during placement. Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved. 2. Specifically, moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the fill material pumping when proof-rolled.